Detailed explanation of Oracle's stored procedures and triggers
Oracle is a well-known relational database management system, often used in the development and maintenance of large enterprise-level systems. In Oracle, stored procedures and triggers are two very important database objects. This article will introduce their functions and how to use them.
1. Stored procedures
1. Function
A stored procedure is a set of SQL statements that are compiled and saved in the database. It can be called like a function, receiving input parameters and returning a result. Stored procedures can complete various complex operations, such as data query, data modification, data backup, etc. They greatly simplify the work of database programming.
2. Create
In Oracle, creating a stored procedure requires the use of PL/SQL language, which can be created and edited using tools such as SQL Developer or SQL*Plus. The following is a simple example of creating a stored procedure:
CREATE OR REPLACE PROCEDURE p_add (x IN NUMBER, y IN NUMBER, z OUT NUMBER) IS BEGIN z := x + y; END p_add;
In the above example, we define a stored procedure named p_add, which has two input parameters x and y, and one output parameter z. In the body of the stored procedure, we add the input parameters x and y and assign the result to the output parameter z.
3. Call
After creating the stored procedure, we can execute the SQL statement in it by calling it. There are two ways to call stored procedures in PL/SQL:
- Use the EXECUTE statement:
EXECUTE p_add(1,2,:OUT);
In the above example, we called the procedure named p_add Stored procedure, pass in parameters 1 and 2, and use OUT parameters to output the results.
- Using PL/SQL block:
DECLARE
a NUMBER;
BEGIN
p_add(1,2,a);
DBMS_OUTPUT.PUT_LINE('The result is: ' || a);
END;
In the above example, we use PL/SQL block to call the stored procedure and output the result.
2. Trigger
1. Function
A trigger is a special object associated with a table that can automatically execute INSERT, UPDATE, and DELETE operations on the table. Perform some actions. Triggers can be used for operations such as data verification, data replication, and data backup.
2. Create
In Oracle, creating a trigger requires the use of PL/SQL language, or you can use tools such as SQL Developer or SQL*Plus to create and edit. The following is a simple example of creating a trigger:
CREATE OR REPLACE TRIGGER trg_ins_emp BEFORE INSERT ON emp FOR EACH ROW BEGIN :NEW.create_time := SYSDATE; END trg_ins_emp;
In the above example, we define a trigger named trg_ins_emp, which changes the current time before each new record is inserted into the emp table. Assign a value to the create_time field.
In the above example, the BEFORE keyword indicates that the trigger will be triggered before data is inserted, and FOR EACH ROW indicates that it will be triggered every time the INSERT statement is executed.
3. Call
After creating a trigger, we do not need to call it manually. We only need to perform INSERT, UPDATE, and DELETE operations on the relevant table to trigger the trigger. The following is a simple example of performing an INSERT operation:
INSERT INTO emp (name, salary) VALUES ('Jack', 5000);
In the above example, we insert a record into the emp table. Since we created a trigger named trg_ins_emp, when inserting the record, The create_time field is automatically assigned the current time.
3. Summary
Stored procedures and triggers are two very important objects in Oracle. They greatly simplify the work of database programming. Stored procedures can encapsulate complex SQL operations, greatly improving the maintainability and reusability of the code. Triggers can automatically perform some operations during table operations to avoid repetitive work. I hope this article can help readers further understand the stored procedures and triggers of Oracle database.
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